Runoff and sediment yield from rural roads, trails and settlements in the upper Konto catchment, East Java, Indonesia

Abstract

The potential importance of roads and settlements for the generation of storm runoff and sediment in tropical steeplands is increasingly recognised but rarely quantified. This paper presents runoff and sediment yield data for a cobbled and an unpaved road section, two large unbounded settlement plots, and several trails draining residential areas or terraced fields in a volcanic upland catchment in East Java. In addition, the sediment yield of major landslides associated with roads was quantified. The unpaved road section exhibited an average runoff coefficient of about 65% and yielded about 7 kg m − 2 yr − 1 of sediment. Both the runoff coefficient and the sediment yield for the cobbled road section (plus adjacent yards) were lower (38% and 1.9 kg m − 2 yr − 1 ). Sediment output from a 4160-m 2 hillside plot including a network of trails draining terraced fields (for which runoff and sediment outputs were shown to be negligible) was similar to that for the cobbled road (2–3 kg m − 2 yr − 1 depending on rainfall). However, a much higher value was obtained when the overall soil loss from the plot was expressed per square metre of trail surface area (ca. 42 kg m − 2 yr − 1 ) whereas the associated trail runoff coefficient was about 70%. The results obtained for several trails and large unbounded plots draining residential areas at two locations were less extreme (runoff coefficients of 24–43%; soil loss 1.3–3.5 kg m − 2 yr − 1 ). Landsliding occurred mainly at the end of the rainy season (March) and was estimated to have contributed ca. 2365 m 3 of sediment to the main road network during the 1988/89 wet season vs. ca. 905 m 3 in 1989/90 and only ca. 150 m 3 in 2000/01. It is concluded that, despite their relatively small areal extent (5% in the study area), rural roads, trails and settlements are significant producers of runoff and sediment at the catchment scale and should be included in watershed management programmes designed to reduce catchment sediment yields and reservoir siltation.